[RTTY] Fwd: [dxlab] Using a 45 Baud Baudot Modem with WinWarbler

[Peter Laws]

Likely of interest - from the DXLab mailing list.


---------- Forwarded message ----------
From: Wes Cosand <wes.cosand at gmail.com>
Date: Mon, Nov 10, 2008 at 15:05
Subject: [dxlab] Using a 45 Baud Baudot Modem with WinWarbler
To: DXLab Yahoo Group <dxlab at yahoogroups.com>


Dave suggested I post my experiences using a hardware RTTY modem.

I am a new user of DXLab Suite and I am very pleased with the
software.  One reason I switched from my previous software is that
WinWarbler uses the MMTTY engine which I consider a very fine decoder.
 However, when I discovered that WinWarbler could have a receive
window for both MMTTY and one for a hardware modem, I went into the
basement and pulled out a Hal ST-8000, an analog military-grade RTTY
modem built in the 1980's, and set it up so that I could read its
output on the second WinWarbler RTTY receive screen.

How Does The Analog Modem Compare to MMTTY
You will find lots of opinions on the amateur email reflectors but in
my experience MMTTY is a very good decoder, at least as good as the
Hal ST-8000 in many circumstances.  (Unfortunately, I have never had
the opportunity to use Brian's RITTY DOS decoder.)  We often
underestimate the value of the AFC feature of RTTY software.  The
squelch function of MMTTY is excellent.  But running both receive
screens one does see conditions where MMTTY takes some hits while the
Hal copies correctly.  So there is real value in having both receive
screens running.  After my experience I am not certain I again would
pay the fairly high price I paid for the "new old stock" Hal on eBay a
few years ago.  It may be that I don't know how to use the unit most
optimally.  There are four AM detector modes and two FM modes and I
usually use only one of these unless there is heavy QRM on either the
space or mark frequency.   It is possible that the filters in my unit
are no longer aligned optimally.  However the Hal repair manual says
that experience has shown that the alignment does not shift and that
the circuits should not be realigned unless some component in the
circuit has been replaced.

But I have always wanted a Hal unit in my shack and my grandson loves
the blinking LEDs and the tuning scope.  The Hal is a lovely unit that
is built to a standard we don't see in ham equipment.  It is fun to
watch the difference in copy between free DSP software and thousands
of dollars of analog filters.  So the Hal will stay in my shack.  But,
there is a SIGNIFICANT ISSUE!

The Issue
The ST-8000, like many RTTY modems, has an RS-232 output that works at
45 baud, lower than most PC software can use.  There are specialized
software that I have used successfully with such units such as
WriteLog and DSRTTY-Win, the Hal Windows terminal program.  But I
wanted my digital terminal program to be tightly integrated with my
general logging program so I sought another solution.

The Most General Solution
I miss the RTTY Journal where these matters were discussed!  But Bob
Boyd, W1VXV, has written up a page which K0BX has posted on his web
site, http://www.qsl.net/k0bx/st8000.htm where he plugs the 45 baud
RS-232 output from the ST-8000 into the "External Modem" input of an
AEA PK-232.  The PK-232, which many of us have sitting around on the
shelf, provides a compatible serial route to the entire world of
Windows RTTY software.  This is the solution I adopted years ago for
the Hal.  Many of us have installed a SPDT switch on the upper right
corner of the front panel of the PK-232 so we can easily switch from
the external modem to the internal RTTY modem of the PK-232 (which is
pretty good, especially if you make the widely used modification to
change the RX shift from 200 hz to 170 hz).  Lots of RTTY contests are
still won by stations using the  PK-232 modem.

I also used this solution with the amateur-grade Hal ST-6000 which, if
I remember correctly, had a TTL output instead of RS-232 so I soldered
a conversion chip from Radio Shack inside the ST-6000 (or was it
inside the PK-232 -- I forget), and then plugged the ST-6000 into the
external modem of the PK-232.  Worked fine.  The PK-232 can be used in
this manner with a number of excellent, older RTTY modems made by
several manufacturers.

A Simpler ST-8000-Specific Solution
If you have a ST-8000 in the basement but you can't find the AEA Molex
external modem connector in your box of discarded cables, there is
another solution.  The ST-8000 has a fascinating "regeneration"
circuit that transforms the decoded receive data stream back into
clean Baudot audio and outputs it on the transmitter AFSK plug on the
back of the unit.  Assuming you are using the WinWarbler FSK or AFSK
output to drive the transmitter, which I would strongly recommend,
simply run an audio cable from the AFSK output of the ST-8000 into the
RX audio input of any Windows compatible hardware RTTY modem.  The
demodulated AFSK receive output will be identical to the RS-232
received data stream.  If you don't have a Windows compatible modem,
run the AFSK audio into a second sound card and use some sound card
RTTY program to decode it.  This also works just fine.  I haven't been
able to get two instances of MMTTY to run but you can always run
another RTTY program along with WinWarbler, even if it isn't as
convenient.

If you work with the Hal ST-8000 you are going to have to set up the
DIP switches correctly to get AFSK to output the received data.  There
are errors in the discussion of DIP switch settings in the 10/1985
Operator's Manual.  Make certain you have the 10/1986 Revisions.

Wes Cosand, WZ7I
www.wz7i.com

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-- 
Peter Laws | N5UWY | plaws plaws net | Travel by Train!

No Trillion-dollar blank check for crooks!